AMD R9-285 Graphics Card

A new GPU for the sub-£200 market

AMD's Radeon Rx 2xx series of graphics cards is primarily constructed from rebranded HD 7000 products, and only the R9 295X2, R9 290X and R9 290 are based on a new GPU family known as Hawaii. There are a couple of new Rx 2xx models that have no direct predecessors in the HD 7000 series and are based on slight modifications to existing GPU designs. The GPUs we are referring to are the R7 260, based on Bonaire design, and the R9 270, based on AMD's Curacao architecture.

Matters become slightly more muddled when you take into consideration revisions to AMD's Graphics Core Next (GCN) architecture. All HD 7000-series GPUs and their associated rebrands can be classified as GCN 1.0, with exception of the Bonaire GPU. The Bonaire GPU, which forms the HD 7790, R7 260 and R7 260X, is a GCN 1.1 design, just like the Hawaii GPU and its spin-offs - the R9 295X2, R9 290X and R9 290.

All GCN 1.1 GPUs share additional features not found on GCN 1.0 silicon. These features include better geometry throughput and an improved memory-controller design as well as bridgeless XDMA CrossFire and TrueAudio support. The newly released Radeon R9 285, codenamed Tonga, takes the GCN design further still, introducing what might be loosely defined as GCN 1.2, which we'll elaborate on shortly.

The R9 285 gets introduced at the upper-mainstream $250 price point as a successor to the current R9 280, itself a rebrand of the HD 7950 released back in January of 2012. The R9 285's price point will be surprisingly familiar to many as Nvidia's GTX 760 also finds itself with a $250 MSRP. Such a price similarity is not a mere coincidence; AMD wants to directly challenge Nvidia's GTX 760 with this release.

Analysis

At a fundamental level the R9 285 shares many of its features with the range-topping R9 290X graphics card since GCN 1.2 inherits GCN 1.1's features such as TrueAudio and XDMA CrossFire. The R9 285 is also physically similar to its predecessor, the R9 280, sporting the same number of GCN cores, texture units and render-output units. The crucial difference with the R9 280 is the trimmed-down memory interface, reduced on this new model from 384 to 256 bits. The die-size and transistor count of the R9 285 ends up being slightly larger than the R9 280, which is surprising given the cut-down memory infrastructure.

A reduction from 3GB of GDDR5 to 2GB paired with less memory bandwidth tops off what seems like an underwhelming GPU from AMD. On paper, at least, the R9 285 should be notably slower than its predecessor, but why doesn't this pan out in reality?

Shouldn't R9 285 be slower - GCN 1.2 to the rescue

The saving grace of the R9 285 Tonga GPU stems from its revised GCN 1.2 architecture. Tonga is able to leverage the efficiency improvements made by both GCN 1.1 and 1.2 to overcome its inferior on-paper specifications. The R9 285 is able to regain some ground by taking advantage of an improved geometry and tessellation engine. Furthermore, the revised process of storing colour data in a lossless format results in up to 40 per cent higher memory-bandwidth efficiency in certain scenarios, according to AMD.

The specifics of the broader GCN 1.2 revision are not explicitly detailed by AMD. The company does, however, reveal a summary of the updated instruction-set that Tonga takes advantage of, including improved compute task scheduling, a 16-bit FP and integer operation block to complete the 32-bit equivalent and data parallel processing instructions.

More specific to Tonga's implementation of GCN 1.2 is the inclusion of vertex reuse, particularly effective with small triangles in triangulated-irregular networks, and improved work distribution on the geometry front-end. Colour compression is dealt with through a new compression method called 'lossless delta color compression'. Crucially for gamers the efficiency improvements relating to geometry and memory bandwidth will be application-dependent. It is reasonable to assume the R9 285 will be neither outright faster nor slower than the R9 280 across a range of gaming tests.

The last GCN 1.2 update pertains to the Unified Video Decoder (UVD) which is now capable of full decoding of 4K at 60Hz compared to 4K at 30Hz in GCN 1.1. Similarly, the Video Coding Engine (VCE) has received an equivalent upgrade for 4K-capability making it AMD's most advanced GPU for encoding and decoding workloads.

A retail card

AMD board partners are already very familiar with what it takes to cool the R9 285 given that its TDP falls in between the long-standing R9 270X and the R9 280. Sapphire's Dual-X variant is a perfect example of this, because Sapphire knows less cooling is needed but reusing its existing cooling solution does no harm and ensures overclocking is well-catered for. Measuring in at 10.5in (262mm) long and presented in the usual dual-slot form factor, Sapphire also includes thermal pads for the memory chips and, probably more importantly, has a small heatsink covering the VRM components situated directly below the right-hand fan.

Summary

AMD's Radeon R9 285 can be best described as a horizontal release for the upper-mainstream market. Benchmarks across the Internet demonstrate the R9 285 performs the same as the equivalently-priced R9 280 it succeeds. Performance does vary slightly across games, as alluded to above, but the R9 285 benefits from a greatly improved feature-set, enhanced power efficiency and a price advantage versus Nvidia's GTX 760.

As always, Scan Computers is selling a wide range of AMD Radeon R9 285 graphics cards. Please head on over to here to peruse our selection.